Induction of the blood-brain barrier-related enzyme alkaline phosphatase in cerebral capillary endothelial cells by neuroectodermal cells in vitro

Abstract

We have investigated the loss of activity of the blood-brain barrier (BBB)-related enzyme alkaline phosphatase (ALP) in primary cultures of porcine brain capillary endothelial cells (BCEC) and the reinduction of this enzyme attained by various cells of neuroectodermal origin. Following the inhibition of ALP-activity by levamisol at different times in vitro we are able to show that the loss of this enzyme activity during cell culture is due to a cessation of its de novo synthesis. The activity of this enzyme can be restored by neuronal and astroglial cells as well as by epithelial cells derived from the choroid plexus, but not by oligodendroglial cells. All of the inducing cells had to be in direct contact with the endothelial cells to be effective. Conditioned media and coculture without direct cell-cell contact were ineffective. Our results imply that among cells of neuroectodermal origin neurons, astrocytes and astrocyte-related cells are able to induce BBB characteristics in endothelial cells in a similar fashion, whereas oligodendroglial cells are unable to do so.